1. Field of the Invention
The present invention relates to systems and methods for conveying carts, pallets or the like in production lines. More particularly, the present invention relates to conveying systems arid methods for production lines where a plurality of carts, pallets or the like loaded with parts are conveyed in contact with each other along a conveying route.
2. Description of the Related Art
An apparatus for conveying a plurality of carts, pallets or the like which are in contact with each other in series is disclosed in the Japanese Unexamined Patent Publication Nos. 2-102865 and 5-85357.
In these conveying apparatuses, a driving conveying unit for driving a cart is disposed along a conveying route, and a braking conveying unit for braking a cart is disposed at downstream of the driving conveying unit. Both conveying units cooperate with one another for smoothly moving plurality of carts to a position near the braking conveying unit while preventing them from separating from each other.
More specifically, as shown in FIGS. 44 and 45, a plate-like driven portion 102 extending in the conveying direction is attached to the underside of each cart 101. In a driving conveying unit 103, the rotation of a drive motor 104 is transmitted to a roller 108A via a shaft 105A, a drive gear 106A and a rotating shaft 107A. The rotation of the drive motor 104 is also transmitted to a roller 108b via the drive gear 106A, a drive gear 106B and a rotating shaft 107B. As a result of such transmission of rotation, two rollers 108A and 108B rotate in the opposite directions. When movement of a cylinder rod 109 causes a lever 110 to pivot, a swing member 112B pivots about a shaft 105B via the shaft 105B and an interlocking gear 111B. A swing member 112A pivots about a shaft 105A via interlocking gears 111B and 111A. The driven portion 102 is clamped by the roller 108A on the swing member 112A and the roller 108B on the swing member 112B, thereby conveying the cart 101, an object to be conveyed, on both rails 113.
In the driving conveying unit 103, the rotary shaft 107A, 107B of each roller 108A, 108B is always axisymmetric with respect to the conveying route 114. Hence, if the extending direction of the driven portion 102 and the conveying route 114 intersect due to an error in mounting the driven portion 102 to the cart 101, the rollers 108A and 108B will impose an excessive force on the driven portion 102. As a result, a load is applied to wheels 115 and the related components of the cart 101, resulting in the unsmooth travel of the cart 101.
Accordingly, it is necessary to precisely mount the driven portion 102 between the rotary shafts 107A and 107B of both rollers 108A and 108B. However, this installation work is quite troublesome, and may consequently increases manufacturing costs.
Furthermore, since the driving and braking units are used for conveying the cart 101, the extension work of a production line requires the adjustment of the spacing between two units. For this purpose, the position of the braking unit is to be changed, or the conveying capability of the conveying unit 103 is to be increased. In the extreme case, additional pairs of conveying units should be provided. This makes the extension work difficult.
Moreover, each cart should contact adjacent carts when be conveyed between the conveying units. This causes a pressing force to constantly act on each cart in the conveying direction. Each cart, therefore, is required to be rigid sufficiently to resist the pressing force, with a resultant increase in manufacturing costs. Another disadvantage is that the driving force of the driving unit is nullified by the counter braking force of the braking unit. Accordingly, the carts should be pushed, preferably under a uniform contact pressure, in the conveying direction for successive conveyance.
Conceivable measures for achieving this object will be discussed below.
For improving the functions of the conveying unit, the following measure is proposed. The rollers may be arranged to press against the driven portion of each cart with a substantially constant force for substantially equalize transmitting the power from the rollers to the driven portion. This allows the conveying speed of each cart to be identical. For this purpose, the rotating speed of rollers pressed against the driven portion may be identical for each conveying unit. As a result, the driven portion unprecisely mounted does not receive any excessive horizontal force, resulting in smooth conveyance of the cart.
An alternative solution is obtained by controlling the rotating speed of each drive motor for conveying all the carts at an identical speed.
These two improvements will facilitate the easy extension work of a production line.
In the production line, the conveying direction may be changed in the midst of conveying pallets. For changing the conveying direction, a dedicated changing device is usually used in addition to the driving and braking conveying units. This is disadvantageous in terms of equipment costs.
The Japanese Unexamined Patent Publication No. 1-192610 discloses an apparatus for changing the direction of pallet conveyance by 180 degrees. In this apparatus, a plurality of shafts are linked for forming a semicircle to convey pallets along each shaft. However, the linkage of a plurality of shafts causes a restriction for minimizing the radius of curvature of the apparatus. Accordingly, the apparatus becomes unnecessarily large.
In a conveying apparatus, as described above, the preceding pallet is pushed by the following pallet, thereby conveying a plurality of pallets in sequence. Hence, when the conveying apparatus operates normally, the adjacent carts should be in contact one with another.
In view of this fact, various kinds of devices are proposed for checking the state of contact between adjacent carts. For instance, the device having a roller along in the conveying route may be in compressive contact with each cart. The rotation of the roller can be detected by an encoder so that the spacing between adjacent carts is calculated based on the detected value, thereby checking the state of contact between carts.
In another example, a device uses an optical non-contact sensor such as an asea sensor to directly detect the spacing between cartes for checking the state of contact between carts.
For the device using the encoder, if slippage occurs between the roller and a cart, the spacing may be calculated from an erroneous value detected by the encoder, and consequently, the checking accuracy deteriorates. Additionally, the need for calculating the spacing makes the control complex, leading to an increase in equipment costs. For the device using a non-contact sensor, foreign matter such as dirt and dust is apt to cause an error or malfunction; hence, this method is poor in reliability.